Utility power devices, such as circuit breakers, oil filled power and distribution transformers, transformer bushings, substation transformers, oil filled voltage regulators, vacuum breakers and reclosers, coupling capacitors, surge arresters, to name a few, operate in high voltages, which are upward of 10 kV and sometimes more than 69 kV. These utility power devices are frequently installed together with other high voltage devices having exposed terminals. Many of these utility power devices may be installed in an outdoor environment, on an elevated platform surrounded by high voltage transmission line cables, or these utility power devices may be obstructed by tree branches or by other utility power devices. Therefore, the ease or their access by the field workers is greatly limited.
In addition, performing routine maintenance checks or fault diagnostics may require testing the utility power devices in both low voltages (under 500V) and high voltages (>500V, typically 1 kV to 15 kV), which may require multiple connecting, disconnecting or reconnecting of both high voltage cables and low voltage cables to the different terminals of the utility power devices. As mentioned above, these utility power devices may be installed in an environment that is hard to access. It is also difficult for the worker to carry the heavy test apparatus to within reach of the utility power devices to conduct the test routines.
For example, FIG. 1A depicts the performance of an exemplary test measurement on a utility power device (150) in a related art method, using a low voltage lead (124) and a high voltage lead (134). The illustrated utility power device (150) may be an oil filled three-phase power transformer.
The utility power device (150) may include two sets of voltage windings, namely, high voltage windings (156) (Delta-connected transformer windings) and low voltage windings (166) (Wye-connected transformer windings). The high voltage windings (156) receive or output a higher voltage than the low voltage windings (166).
The high voltage windings (156) are wound on three nodes (H1A, H2A and H3A) with each of the three nodes (H1A, H2A and H3A) being 120 degrees out of phase from each other. Likewise, the low voltage windings (166) are wound on three nodes (X1A, X2A and X3A) with each of the three nodes (X1A, X2A and X3A) being 120 degrees out of phase from each other. In addition, the low voltage windings (166) include a neutral node XOA. The currents of the nodes H1A, H2A and H3A on the high voltage windings (156) may return via respective nodes X1A, X2A and X3A of the low voltage windings (166). The operating principle and manner of construction of a three-phase power transformer are generally known in the art.
Each of the nodes (H1A, H2A and H3A) in the high voltage windings (156) may be electrically coupled to respective high voltage bushings (H1, H2 and H3) as external terminals. Likewise, each of the nodes (XOA, X1A, X2A and X3A) in the low voltage windings (166) may be electrically coupled to respective low voltage bushings (X0, X1, X2 and X3) as external terminals. Each bushing is constructed to include a center conductor (e.g., 171) overlayed with with multilayer dielectric insulating materials, thus forming a capacitive bushing (e.g., H1). The bushings are rated for high voltage operations (>69 kV), and may be hermetically sealed to protect the center conductor and the multilayer insulating dielectric materials from exposure to the ambient atmosphere, which may cause degradation and shortening of their service life. Water shed discs (178) are formed on the bushing to help divert rain, snow or to help dissipate heat.
In addition, a tap electrode (e.g., Tp1, Tp2 or Tp3) is located at the base of the bushing (H1, H2 or H3) to provide electrical contact for evaluation of the integrity of the multilayer insulating dielectric materials within the bushing. The tap electrode (e.g., Tp1, Tp2 or Tp3) is normally covered, and the cover may be grounded to the chassis of the utility power device (150). The grounded cover may be removed to expose the tap electrode (Tp1, Tp2 or Tp3) to facilitate electrical contact with the tap electrode at the time of testing. More details about the electrical model of the bushing and the testing may be found in chapter three of the “Doble Test Procedures”, which is incorporated by reference.
An exemplary apparatus (100) for performing multiple test measurements on the utility power device (150) is illustrated in FIG. 1A. The exemplary apparatus (100) includes a processor (112), which executes instruction code stored in at least one memory (113). The processor (150) may also execute an application (117) stored in the memory (113) to carry out the test routines on the utility power device (150). The processor (112) may also configure a switching matrix (118) to perform operations such as the sourcing of low voltage signals (e.g., <500V, typically up to 250V) via anyone of ports LVS1 (122a) to LVSn (122n), and the sourcing of high voltage signals (e.g., >500V, typically 1 kV to 15 kV) via port HV (132).
Return signals from high voltage excitation or low voltage excitation test measurements may be received via a low voltage lead (124) to anyone of the low voltage measurement ports LVM1 (123a) to LVM 3 (123c). In addition, a ground lead (126) from the TEST-GND port (121) of the apparatus (100) may be electrically coupled to the chassis ground (168) of the utility power device (150) to measure return ground currents of the utility power device (150).
Depending on the type of test measurement, currents measured from the low voltage lead (124) and from the ground lead (126) may be summed together by the apparatus (100). In certain test measurements, the TEST-GND port (121) or one of the low voltage measurement ports LVM1 (123a) to LVM 3 (123c) may be selectively routed internally by the switching matrix (118) to a guard point (128) within the apparatus as a by-pass current return path (i.e., the by-pass currents will not be measured). The guard point (128) signifies one or more conducting elements as return nodes internally connected on the apparatus (100), which may be used by the measurement unit (115) to divert (i.e., by-pass) unwanted currents from the measurements.
FIG. 1A also illustrates an exemplary test setup for conducting test measurements on the utility power device (150), such as a power factor (PF) test in the related art. The power-factor test measurement is specified in section 10.10.4 of the IEEE Std C57.12.90-2010. Power factor test measurements performed on the utility power device (150) at the factory are compared with power factor test measurements performed at the field to assess a probable condition of the internal insulation within the utility power device (150).
The setup in FIG. 1A may also short circuit the windings in both the high voltage windings (156) and the low voltage windings (166) to eliminate winding inductance when measuring internal insulation of the utility power device (150). The short circuiting may be achieved by using a conductive bus wire (174) to short circuit the conductors (171, 172 and 173) of the high voltage bushings (H1, H2 and H3), and using a conductive bus wire (184) to short circuit the conductors (180, 181, 182 and 183) of the low voltage bushings (X0, X1, X2 and X3), respectively.
Unless otherwise stated, it is understood that prior to the start of any test measurements in this disclosure, the apparatus (100) and the utility power device (150) are both electrically grounded to a common ground (i.e., an earth gound by default).
Section 10.10.4 of the IEEE Std C57.12.90-2010A specifies a typical power factor test on an oil filled two winding transformer, such as the utility power device (150) illustrated in FIG. 1A. Using the related art method, the complete power factor test may be carried out via a first procedure (see FIG. 1A) and a second procedure (see FIG. 1B). The order in which the two procedures are performed is unimportant. The first procedure may be performed on the high voltage winding side (156), and the second procedure may be performed on the low voltage winding side (166).
The first procedure may be carried out with the following exemplary steps:
(1) Placing the high voltage lead (134) on the bus wire (174) of the high voltage windings (156) (i.e., to all three terminals on the Delta-connected transformer windings), placing the low voltage lead (124) on the bus wire (184) of the low voltage windings (166) (to all three terminals on the Wye-connected transformer windings), and electrically coupling the TEST-GND port (121) of the apparatus (100) to the chassis ground (168) of the utility power device (150) via the ground lead (126).                (a) Configuring the switching matrix (118) to connect the low voltage lead (124) to TEST-GND port (121) (i.e., by routing the low voltage measure port LVM1 (123a) to the TEST-GND port (121)).        (b) Configuring measurement unit (115) to measure current to the TEST-GND port (121) (i.e., measuring electrical parameters on both the current from the ground lead (126) and the low voltage lead (124) via port LVM1 (123a)).        (c) Sending or applying a high voltage signal (HV) from the high voltage port HV (132) via the high voltage lead (134) to the bus wire (174) of the high voltage windings (156). Measuring the applied high voltage signal (HV), and the current in the measurement unit (115) (i.e., measuring electrical parameters on both the current from the ground lead (126) and the low voltage lead (124)).        
(2) Continue with the same leads (124, 134, 126) arrangement for the set up configuration as in FIG. 1A:                (a) Configuring switching matrix (118) to connect the low voltage lead (124) to GUARD point (128) (i.e., by internally routing the low voltage measure port LVM1 (123a) to the GUARD point (128) to by-pass the current in the low voltage lead (124)).        (b) Configuring measurement unit (115) to measure current to TEST-GND port (121).        (c) Sending or applying a high voltage signal (HV) from the high voltage port HV (132) via the high voltage lead (134) to the bus wire (174) of the high voltage windings (156). Measuring electrical parameters on the applied voltage (HV), and the current in the measurement unit (115) (i.e., measuring electrical parameters on only the current from the ground lead (126).        
(3) Continue with the same leads (124, 134, 126) arrangement for the set up configuration in FIG. 1A:                (a) Configuring switching matrix (118) to connect TEST-GND port (121) to GUARD point (128) (i.e., by routing the TEST-GND port (121) to the GUARD point (128) to by-pass the current in the ground lead (126)).        (b) Configuring measurement unit (115) to measure current to the low voltage lead (124).        (c) Measuring applied voltage (HV), and the current in the measurement unit (115) (i.e., measuring electrical parameters on only the current from the low voltage lead (124)).        
The second procedure of the power factor test on the low voltage winding side may be carried out by repeating the identical steps (1) to (3) in the first procedure, using a setup configuration as illustrated in FIG. 1B. The configuration between the setup in FIG. 1A and FIG. 1B are different in that a) the high voltage lead (134) is now connected to the bus wire (184) of the low voltage windings (166), and b) the low voltage lead (124) is now connected to the the bus wire (174) of the high voltage windings (156). In other words, a high voltage signal (HV) may be applied from the high voltage port HV (132) via the high voltage lead (134) to the bus wire (184) of the low voltage windings (166), and measurements of electrical parameters may be taken via the low voltage lead (124) on the bus wire (174) of the high voltage windings (156).
It should be noted that the test setup configuration according to both FIGS. 1A and 1B would require the field worker to stop at the completion of steps (1) to (3) to regain access to the utility power device (150) to reverse the high voltage lead (134) and the low voltage lead (124) on the respective bus wires (174, 184). In this regard, the testing time may be lengthened, and the field worker may be exposed to the hazardous high voltage surroundings while attempting to regain access.
The problems above are exacerbated with the test measurements illustrated in FIGS. 1C and 1D. Similar to FIGS. 1A and 1B, the test measurements of FIGS. 1C and 1D may be power factor tests or insulation condition tests on the high voltage bushings (H1 to H3) and on the low voltage bushings (X1 to X3). The test measurements of FIGS. 1C and 1D may be viewed as two separate procedures of a complete test routine. More specifically, FIG. 1C represents a test setup configuration in a related art method, using a low voltage lead and a high voltage lead to measure the power factor of each of the high voltage bushings (H1, H2 and H3) and the low voltage bushings (X1, X2 and X3) on the utility power device (150).
The setup configutration in FIG. 1C may be similar to FIG. 1A in many aspects, including: short circuiting of both the high voltage windings (156) and the low voltage windings (166) to eliminate winding inductance when measuring internal insulation of the high voltage bushings (H1, H2 and H3) and the low voltage bushings (X1, X2 and X3), using the conductive bus wires (174 and 184) for the high voltage bushings (H1, H2 and H3) and the low voltage bushings (X0, X1, X2 and X3), respectively. Prior to the start of the test measurements, the apparatus (100) and the utility power device (150) are both electrically grounded to a common ground (i.e., an earth ground by default).
A typical power factor test performed on the high voltage bushing (H1, H2 and H3) in the related art may be carried out as with the following steps:
(1) Placing the high voltage lead (134) on the bus wire (174) of the high voltage windings (156) (i.e., to all three terminals on the Delta-connected transformer windings), connecting the low voltage lead (124) to the tap electrode (Tp1) of bushing H1, and electrically coupling the TEST-GND port (121) of the apparatus (100) to the chassis ground (168) of the utility power device (150) via the ground lead (126).                (a) Configuring switching matrix (118) to connect TEST-GND port (121) to GUARD point (128) (i.e., by internally routing the TEST-GND port (121) to the GUARD point (128) to by-pass the current in the ground lead (126)).        (b) Configuring measurement unit (115) to measure current to the low voltage lead (124).        (c) Measuring applied voltage (HV), and the current in the measurement unit (115) (i.e., measuring only the current returned from the low voltage lead (124)).        
(2) Continue with the same leads (134, 126) arrangement for the set up configuration as in FIG. 1C, except connecting the low voltage lead (124) to the tap electrode (Tp2), and repeat the same tests (1a-1c) for the bushing (H2).
(3) Continue with the same leads (134, 126) arrangement for the set up configuration as in FIG. 1C, except connecting the low voltage lead (124) to the tap electrode (Tp3), and repeat the same tests (1a-1c) for the bushing (H3).
(4) Placing the low voltage lead (124) on the bus wire (174) of the high voltage windings (156) (i.e., to all three terminals on the Delta-connected transformer windings), connecting the high voltage lead (134) to the tap electrode (Tp1) of bushing H1, and electrically coupling the TEST-GND port (121) of the apparatus (100) to the chassis ground (168) of the utility power device (150) via the ground lead (126).                (a) Configuring switching matrix (118) to connect the low voltage lead (124) to GUARD point (128) (i.e., by internally routing the low voltage lead port (LVM1) (123a) to the GUARD point (128) to by-pass the current in the low voltage lead (124)).        (b) Configuring measurement unit (115) to measure current to the TEST-GND port (121).        (c) Measuring applied voltage (HV), and the current in the measurement unit (115) (i.e., measuring only the current returned from the ground lead (126)).        
(5) Continue with the same leads (124, 126) arrangement for the set up configuration as in FIG. 1C, except connecting the the high voltage lead (134) to the tap electrode (Tp2), and repeat the same tests (4a-4c) for the bushing (H2).
(6) Continue with the same leads (124, 126) arrangement for the set up configuration as in FIG. 1C, except connecting the low voltage lead (134) to the tap electrode (Tp3), and repeat the same test tests (4a-4c) for the bushing (H3).
It should noted that carrying out steps (1) to (3) requires changing the low voltage lead (124) to the subsequent tap electrode twice. Likewise, carrying out steps (4) to (6) also requires changing the high voltage lead (134) to the subsequent tap electrode twice. Swapping of the various leads (i.e., high voltage lead (134) with the low voltage lead (124) in step (4)) results in at least five interruptions for field worker. That is, the field worker would be exposed to a hazardous high voltage surrounding at least five times.
FIG. 1D depicts the same power factor test measurements on the low voltage bushings (X1 to X3) of the low voltage windings (166) using a similar test setup configuration as in FIG. 1C, except that the high voltage lead (134) is now connected to the bus wire (184) of the low voltage windings (166), and the low voltage lead (124) is now connected to the tap electrode (Tp4) of bushing X1. Accordingly, the second testing procedure of steps (1) to (6) are applicable to the test measurements. That is, there would be at least five interruptions during which the field worker would be exposed to a hazardous high voltage surrounding. Therefore, the field worker is exposed to interruptions and dangerous conditions a total number of ten times in the above test.
The voltage signal sent to the electrode taps (Tp1-Tp6) in carrying out steps (4) to (6) may be carried out at a lower voltage (e.g., 250V). In this regard, the high voltage port (132) may source a lower voltage (e.g., 250V). Alternately, steps (4) to (6) may be carried out using an second low voltage lead sourced by a low voltage port LVS1 (122a) that energizes electrode taps (Tp1-Tp6).
Nevertheless, irrespective of whether the steps (4) to (6) in FIG. 1C or 1D are carried out using the same high voltage lead (134), or alternately using a second low voltage lead sourced by a low voltage port LVS1 (122a) (not shown), the field worker still needs to stop at least ten times to complete both test procedure using the test set up configuration as in FIGS. 1C and 1D.
To summarize the problems in the related art method, testing of the utility power device using the related art methods requires more frequent changing of the voltage leads and, therefore, more frequent interruptions to the workflow. Thus, the known methods take a relatively long time to complete. They are also more prone to human error given that worker fatigue may be an issue, especially when the working environment is not well lit, which would be the case at night during a power outage. In addition, the more frequent accessing of the utility power device to change voltage leads results in an increased risks to the worker of injuries or even accidental death resulting from electrocution.